Finally got my 3.73s installed today. I have to say, they make a huge difference. The car feels so eager and responsive now. I really love the feel.

Now for the possible downside...

I hear a faint whine as I begin acceleration. I don't hear it as I get all the way into it because the motor and exhaust are probably masking it. The sound follows the same pattern as some manual transmissions in reverse. The sound itself is higher pitch and much more faint than the sound forein cars make in reverse.

The sound is most prominent in 1st and 3rd gear on slow steady accel. No evidence of whine etc cruising at 80 or when hammering it to 120 although it is possible the noise is masked by the exhaust as I mentioned earlier.

It may be nothing. I will admit I am listening trying to hear anything abnormal and probably never listened that closely before the gear install.

So, am I hearing gear whine or am I nuts? I will take it to the dealership again but, as we all know, most service techs are deaf as a stone when it comes to hearing noises on customer's cars.

BTW, gears are Ford OEM and installed by Ford techs at a Blue Oval dealership. ECU was reflashed afterwards.

Runs about 2400-2500rpm cruising at 80.

 

probably not shimmed right.

 

Can you elaboarate shadow? Is that something they would have to go back into the yoke to fix?

 

What he probably means is remove the rear differencial cover and re-adjust the backlash of the pinion and gear. They may be off a little, and let me tell you it doesn`t take much to get gear whine noise. Did you have this noise with previous gear set ?

 

I don't think so. I'll show it to the tech tomorrow and hope they hear it too and can fix it.

 

I had 3.90s installed and the shop coundt get it installed without any noise, They took out the Motive gears and Installed Ford 3.73s and they turned out perfect,no noise what so ever. Last Year Ford dealership installed 3.55s and the got them perfect as well, But the Motives howled and made noise,..
If, the were done at Ford and used Ford parts ,they should be silent as they were before.

 

That's why I'm glad my car has at least 3.55 gears. I will not be installing anything different and won't have to worry about whine.

But that's always a risk. I know a couple shops that do great work but sometimes gear whine still happens even with them.

I think even after a correct setup, if the gears whined before, they will always whine because the "pattern" has already been worn into them. That's how it worked on my Camaro. Also a brand new Moser 9" setup by them whined.. hah

 

Coming from an 07 GT that had 4.10 gears go bad...

If you have rear gear troubles, you will know it. It was FAR from a slight whine. My car gave me a headache if i drove it more than 30 minutes on the highway

I dont think its worth taking the diff apart for only a "slight" whine

 

I had mine done recently and notice a bit of woam woam woam noise when OFF the throttle and in gear, but I also installed a Steeda UCA with a new bracket, so that is probably adding some noise.



Does the diff fluid need to be changed after break in of new gears or should it be good to go?

 

I've heard the OEM gears do this in 1st and 3rd as well, in a factory optioned 3.73 car. It was unsettling a little bit and made me think that I'd probably never go with a 3.73 set up.
The 3.55's were beautifully smooth.

 

Sounds like you probably should have waited and ordered a factory 3.73 car.

 

Not true, see above your post.

 

You should be able to get the gears installed without whine. The key to the proper installation is getting both the pinion depth and the backlash between the gears correct. This backlash comes from the lateral positioning of the ring gear. The one way to know for sure is by using paint to mark the gears and observe the meshing of the gears as they are rotated. The pattern of contact tells the story. Unfortunately to do the paint test at this point means draining the diff, removing the cover, and cleaning all the oil off of the gear teeth. There may be another method to see the meshing, but paint was the one I used back in the day.

It can take a lot of time/labor to get the pinion depth set right. I assume that this is the reason why some shops will get the car out the door with a 'just good enough' setup. Otherwise the installation would be very expensive (to either the customer or the shop). A good shop will have invested in the tooling necessary to measure the pinion depth more accurately. The shop that does the setup should have all the available thicknesses of shim stock, without that it can be hard to get the gears just right.

And it is true that there can be some gear whine from the factory, that is why there are two metal weights are attached to some diffs.

 

I would like to see if the BOSS is any different. Since the car only comes with one rear end option maybe more finesse is applied rather than the regular cookie cutter slap in said gear ratio approach.

 

I don't think it has anything to do with the gears you're running, it is the way they are adjusted from the factory. My 3.73 gear set up is as smooth as butter. I would just bring the car to the dealership, maybe all it needs is a little more friction modifier additive. In a lot of occasions it'll take care of the whining noise.

 

It was only coincidence that the car with the 3.73's I had driven had a whine. I am not making the association with a certain gear ratio necessarily but just stating that a whine can come even if the gears are put in upon assembly. The only association I have is that the gears are the same. If he had said 3.55's he installed have a bad whine in 1st and 3rd, I'd have said oh, I heard the same on the 3.73's but the 3.55's were great. I am interested in all the fix methods being thrown around, these topics really interest me.

 

Fix 1 ) Get to dealership and have it fixed under warranty
Fix 2) If installed by local shop, they need to retool and do the job right.

Have a friend that works at one of the biggest Ford dealership in the greater Montreal area, he sells and mods a lot of 2011 GT's with 3.73's and asked him about any issues with gear whine noise.
Not one complaint so far. Just sayin'. All is fine with all the 2011 GT owners i know of that are running the 3.73's. Maybe just a bad batch. First thing a Ford technician will do is put in a bit more additive in the differencial, that should resolve the whining issue if the gears are proprely meshing together.
But i do get your point.

 

Touche.

 

Just go back and have them listen to them. They will or should make it right, Ive had 5 sets in my car already, The most recent is 3.73 and the are quiet ,just like new, Last years Ford put in 3.55s and they were quiet also..
2 of the 5 made noise, 3.90s (Motive Straight cut) and 4.10s>>> Bad install

 

Thanks guys. I have an appt Wednesday to have them look at it again. I think I may also have "the tick" coming from the passenger side front wheel well. Service advisor listened to it when I picked up the car from the gear install and said "I think we should look into that."

Neither issue is that noticeable and they don't affect driveability. Car runs smooth and strong. I'm enjoying her. New wheels and tires go on tomorrow...be on the lookout for pics.